1. Field of the Invention
The present invention relates to a D-class signal amplification circuit that amplifies a power of an input signal of an audio regenerative signal and so forth.
This application is counterpart of Japanese patent application, Ser. No. 317831/2003, filed Sep. 10, 2003, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
A conventional audio signal-reproducing unit includes a delta-sigma modulator as a D/A conversion circuit and a D-class amplifier composed of a CMOS inverter. This type of audio signal-reproducing unit converts the input signal (original signal) being a multi-bit digital signal into one-bit analog signal by means of the delta-sigma modulator, and amplifies this analog signal by means of the D-class amplifier to drive a speaker, etc.
Since an AB-class power amplifier uses an operational amplifier, the amplifier is able to eliminate the fluctuations of a power supply voltage. However, the D-class amplifier composed of a CMOS inverter transfers the power supply voltage to an output side directly, accordingly the amplifier cannot eliminate the fluctuations of the power supply voltage at all. Therefore, to realize a satisfactory sound quality requires an extremely high precision in the power supply voltage of the D-class amplifier. To achieve such a power supply voltage requires a large capacitor and inductor, which is a hindrance to reduce the circuit area and the production cost.
The patent document, i.e. JP-A 2000-536903 (page 11-25, FIG. 2-FIG. 12) discloses an example of the b-class amplifier having a construction that reduces an influence by the fluctuations of the power supply voltage. This D-class amplifier detects an absolute value of noises contained in the output signal, calculates a digital correction signal on the basis of this absolute value, multiplies the input signal by this correction signal, and thereby restrains the influence by the fluctuations of the power supply voltage.
The D-class amplifier disclosed in JP-A 2000-536903 calculates the digital correction signal by use of the absolute value of noises contained in the output signal, which requires a complicated arithmetic operation. The amplifier requires an analog/digital converter (ADC) and so forth to generate the digital correction signal from the analog signal, which complicates the circuit construction and involves an apprehension of the cost increase.